Ball valve having convex seat

Abstract

A valve includes a valve ball and a convex metal valve seat ring that abut along a circle in a metal-to-metal seal. At very high contact forces, the valve ball and/or the valve seat elastically deform to increase the contact area between them and thereby lower the contact pressures applied to the valve ball and valve seat. The valve ball and valve seat are made of materials that do not pressure weld under a wide range of contact pressures. In one embodiment, the valve ball is a stainless steel alloy having a hardness of at least Rockwell 44C and the valve seat is Stellite having a hardness of at least Rockwell 50C. In another embodiment, the valve ball and seat ring are steel alloys having hardnesses above Rockwell 50C.

What is claimed is:  
     
       1. A valve comprising 
       a valve body having a conduit extending therethrough for delivering fluid from a first end toward a second end;  
       a valve ball providing a spherical segment mounted in the valve body for rotation between flow permitting and flow blocking positions for controlling flow through the conduit, and  
       a convex metal valve seat rigidly abutting the valve body at least against the second end and sealingly engaging the spherical segment of the valve ball along a circle for sealing against fluid flow through the valve upon rotation of the valve ball to the flow blocking position.  
     
     
       2. The valve of claim  1  wherein the valve ball and the valve seat are unlapped. 
     
     
       3. The valve of claim  2  wherein the valve ball is made of a steel having a hardness of at least Rockwell 44C and the valve seat is made of a material having a hardness of at least Rockwell 50C for minimizing galling. 
     
     
       4. The valve of claim  3  wherein the metal seat is Stellite. 
     
     
       5. The valve of claim  4  wherein the valve ball is of stainless steel having a hardness of at least Rockwell 44C and the Stellite valve seat has a hardness of at least Rockwell 50C. 
     
     
       6. The valve of claim  1  wherein the valve ball and the metal seat have comparable hardnesses of at least Rockwell 50C. 
     
     
       7. The valve of claim  1  further comprising a second convex metal valve seat sealingly engaging the spherical segment of the valve ball along a circle for sealing against fluid flow through the valve upon rotation of the valve ball to the flow blocking position and means resiliently forcing the second valve seat against the valve ball. 
     
     
       8. The valve of claim  1  wherein the convex valve seat has a radius of curvature of at least 75% of a radius of the valve ball. 
     
     
       9. The valve of claim  1  further comprising a spring between the valve body and the convex seat operating to bias the convex seat toward the second end of the valve body. 
     
     
       10. The valve of claim l wherein the first end of the valve body is an upstream end and the second end is a downstream end. 
     
     
       11. In combination, a valve ball providing a spherical segment mounted for rotation between flow permitting and flow blocking positions for controlling flow, the valve ball being made of a steel alloy having a hardness of at least Rockwell 44C; and 
       a convex unlapped metal seat abutting and sealingly engaging the spherical segment of the valve ball along a circle for sealing against fluid flow upon rotation of the valve ball to the flow blocking position, the seat being made of a material having a hardness of at least Rockwell 44C.  
     
     
       12. The valve of claim  11  wherein the metal seat is Stellite. 
     
     
       13. The valve of claim  11  wherein the valve ball is of stainless steel having a hardness of at least Rockwell 44C and the valve seat has a hardness of at least Rockwell 50C. 
     
     
       14. The valve of claim  11  wherein the valve ball and the metal seat have comparable hardnesses of at least Rockwell 50C. 
     
     
       15. The valve of claim  11  wherein the convex valve seat has a radius of curvature of at least 75% of a radius of the valve ball. 
     
     
       16. In combination, a valve ball providing a spherical segment mounted for rotation between flow permitting and flow blocking positions for controlling flow; and a convex seat abutting and sealingly engaging the spherical segment of the valve ball along a circle for sealing against fluid flow upon rotation of the valve ball to the flow blocking position, the seat and valve ball abutting on a predetermined contact area under no load, being made of materials having predetermined first and second compressive elastic limits and having a pressure rating sufficient to produce a calculated contact pressure between the valve ball and seat above at least one of the first and second compressive elastic limits, the geometry of the valve ball and convex seat acting to increase the contact area under load and thereby maintain the valve ball and seat below the first and second compressive elastic limits at the pressure rating. 
     
     
       17. The combination of claim  16  wherein the valve ball is a steel alloy having a hardness of at least Rockwell 44C and the seat ring is a metal alloy having a hardness of at least Rockwell 50C. 
     
     
       18. The combination of claim  16  wherein the valve ball and the seat ring are steel alloys having comparable hardnesses of at least Rockwell 50C. 
     
     
       19. The combination of claim  16  wherein the valve ball and valve seat are untapped. 
     
     
       20. The valve of claim  16  wherein the convex valve seat has a radius of curvature of at least 75% of a radius of the valve ball. 
     
     
       21. A valve having a rated fluid pressure, comprising 
       a valve body having a conduit extending therethrough for delivering fluid from a first end toward a second end;  
       a first valve member comprising a valve ball providing a spherical segment mounted in the valve body for rotation between flow permitting and flow blocking positions for controlling flow through the conduit,  
       a second valve member comprising a convex valve seat ring mounted in the valve body for sealingly engaging the spherical segment of the valve ball along an annulus of predetermined area, at atmospheric pressure, for sealing against fluid flow through the valve upon rotation of the valve ball to the flow blocking position,  
       the rated fluid pressure divided by the predetermined area of the annulus valve ball and valve seat providing a contact pressure of at least 300,000 psi,  
       the valve ball and valve seat being made of metals plasticly deforming at less than the contact pressure,  
       the valve ball being movable between the flow blocking and flow allowing positions at the rated pressure without inelastically deforming either valve member by elastically deforming at the rated pressure to increase the area of the annulus and thereby decrease the contact pressure between the valve ball and valve seat below the elastic limit of the metals.  
     
     
       22. The valve of claim  21  wherein the rated fluid pressure is at least 10,000 and the valve ball has an inner diameter of at least 2 inches. 
     
     
       23. The valve of claim  21  wherein the surface hardness of the valve ball and the valve seat are at least Rockwell 44C. 
     
     
       24. The valve of claim  21  wherein the convex valve seat has a radius of curvature of at least 75% of a radius of the valve ball. 
     
     
       25. A method of operating a valve comprising a valve body having a conduit extending therethrough for delivering fluid from an upstream end toward a downstream end; a valve ball providing a spherical segment mounted in the valve body for rotation between flow permitting and flow blocking positions for controlling flow through the conduit, and a convex metal valve seat rigidly abutting the valve body sealingly engaging the spherical segment of the valve ball along a circle for sealing against fluid flow through the valve upon rotation of the valve ball to the flow blocking position, the valve ball and seat abutting in a predetermined contact area at atmospheric pressure, comprising the steps of 
       subjecting the valve to a pressure of at least 5,000 psi and elastically deforming the ball valve and seat to increase the contact area above the predetermined contact area.